This invention relates to implantable cardiac pacing apparatus and more particularly to a plug or closure which seals an electrical terminal block of such a pacing apparatus so as to be impervious to bodily fluids while permitting ready access to the terminal block for securing a cardiac lead or for electrical testing.
Cardiac pacemakers are employed to stimulate heart muscle when the body's own stimulatory pathways have become damaged as by disease. The electrical signals from the pacemaker regulate the heart rhythm so that the heart pumps much as it would were it under the control of a normal body's own cardiac nerve impulses. The pacing device is usually implanted beneath the skin of the patient at a location some distance from the heart. The electrical signals generated in the pacing device are transmitted from the device to the heart through an insulated conductor. One end of the conductor is thus attached to the pacing device, and the other end is attached to the heart muscle directly.
Because implantable pacing devices run on self contained batteries, the pacers must be replaced periodically when the batteries have run down. The lead from the pacer to the heart muscle, however, is usually left in place so that it is desirable to be able to disconnect the lead from the pacer at the pacer itself. In this way, the pacer can be removed leaving the lead intact, and another pacer inserted and reconnected to the same lead. Typically, the lead is attached to the pacing device at an electrical terminal block by means such as a set screw. Thus, when it is time to change the pacer, the set screw is loosened thereby allowing the lead to be disconnected from the terminal block. The new pacer is then inserted and the lead reattached to the terminal block by the set screw. It is important for reliable pacer operation that the set screw which holds the lead in electrical contact with the terminal block be shielded from fluids within the body. Such shielding protects the set screw, the terminal block and the lead from corrosion, from electrical leakage and from the accumulation of solid body materials which could interfere with the removal of the set screw when it is time to replace the pacing device. Currently known sealing devices have proved unsatisfactory for the longer term service available with newer pacing devices by allowing seepage into the terminal block of body fluids. Another disadvantage of presently known sealing devices is that they preclude access to the set screw once they are in place. Thus, when inserting a new pacing device, the set screw must be tightened, and thereafter the seal is put into place. This procedure often results in contamination and precludes permanent installation of the seal plug at the time of pacer manufacture. Also, once a pacer is in place and connected to the cardiac lead it is often desirable to make electrical contact with the set screw for testing purposes. In the prior art seals such probing was not possible while the seal was in place.
It is therefore an object of the present invention to provide a superior seal which is mechanically self-sealing and which is substantially impervious to body fluids throughout the lifetime of the pacing device.
A further object of the invention is such a seal which, when in place, still allows access to the set screw for electrical probing or for tightening or loosening the set screw when it is time to replace the pacing device.